In the field of dentistry, a wide variety of procedures and techniques require fabricating a model of a patient's teeth. Modelling teeth often requires making accurate dental casts of a patient's teeth, tooth surfaces, gingival and other fine details of the patient's dentition. Traditional dental casts are made by inserting a dental impression tray with dental impression material into a patient's mouth and keeping it there until the impression material has sufficiently hardened. Then the tray with the impression material is removed from the mouth, the hardened material now containing an impression of the desired intra-oral surfaces of the patient. The impression may then be used for obtaining a positive 3-D model of the dentition. Nowadays, besides the physical 3-D models like plaster casts of teeth, also digital 3-D models are used. In other words, by means of a computer program, negative dental impressions may be used to generate positive digital models of the dentition.
In order for the digital model to have true therapeutic use, in addition to mere general visualization of the intra-oral surfaces, it should be accurate enough. For example, in orthodontics and with other dentistry operations, such as designing tooth transplantations, occlusion corrections, crowns, a high degree of accuracy and detail of the 3-D model is required so that a crown, for example, will fit into the existing dentition properly. Typically, these 3-D digital models are created by using optic scanners utilizing visible light, such as a laser beam, to provide input to a computer program creating the digital 3-D model from the impression. The reason for using optic scanners is that the accuracy achievable by an optical scanner is in the range of microns, such as 0.01 to 0.05 mm, whereas the accuracy of traditional CT (computed tomography) imaging when creating such surface models is in the range of millimeters. A problem with using optical scanners is that its use does not extend to radiography, meaning in practise that two different imaging devices are needed at a dental clinic in order to be able to properly image both cranial surface and sub-surface features.